I've kept them all, misscarriages, too.
I too kept all each of mine, but usually only until they faded! HA! I didn't realize, at first, that with time, some of the tests will fade so that you can no longer see the lines.
This time around I photographed the positive HPT and actually created a scrapbooked page about the experience of discovering for the 8th time that we were pregnant...and praying that we would have a 3rd child.